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Solar hot water and the missing washing machine

Posted by Alister Scott on 9 March 2012 at 10:20 am

Ten years ago we installed solar hot water heating. It's been great, particularly as energy prices have gone up. 

When we did it, I had one professor of environmental policy (who shall remain nameless) look down his nose at me and say "but surely it'll never be economic?" That was telling - talk about economists knowing the price of everything and the value of nothing!

Anyway, I digress. Last year we needed to replace our war horse of a washing machine - 20 years and counting - and could find not a single machine that would accept hot water. 

As more and more people install solar, surely there is a gap in the market for a maker that recognises that people will want to use their free hot water from the sun? Any thoughts welcome.

Photo by Marcelo Nava

About the author: Alister Scott is co-Founder of

If you have a question about anything in the above blog, please ask it in the comments section below.

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20 comments - read them below or add one


jimzjazzComment left on: 17 October 2013 at 9:05 pm

Having been running for 4 weeks@  4 different types of wash per week,I think it is quite safe to say that every part of my installed system is working according to how I envisaged it would ( or perhaps should). I have now settled allowing the shower mixer valve to do its job, firstly, by selecting the washing machine 'type of wash' which gives me an approximate temperature to set the mixer valve, and I leave it at this setting to also do the rinse, I never remember my Mother ( or anyone elses Mother) doing a cold water rinse in the old kitchen sink clothes wash as it was to damn cold 'North of the Border' to go round getting frost bite hands by doing this, so as far as I am concerned this is another washing machine manufacturers to justify there cold water fill machines and if you are concerned about damage to the machine, just think of oily dungarees being washed in a hot wash! as your machine will =with the heater fitted will reach higher temperatures than the setting on my Immersion

So go for it, and you can also use cheaper detergent an forget all about the great Con of cold  temperature soaps and cold fill machines 


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jimzjazzComment left on: 28 September 2013 at 12:16 pm

Having flooded the kitchen floor by trying to fill my cold water fill washing machine by using  hot waterand a  hose pipe as recomended by some one, I decided to buy a  Bristan shower mixer+two full bore level ball valves and using this to supply hot water to my 'cold water fill washing machine' 

It seems to work perfectly, and I could have saved money by buying a cheaper mixer unit -in my ignorance- I have tried different methods of operation ( as with the Immersun diverting lots of power into the existing cylinder, I have lots of hot water available , I  am now leaving the mixer in the highest hot water position for the washing and rinsing cycle( as the cold water rinse shows no benefit to the wash ) and this saves the hassle of changing the mixer position to cold water after the hot water is in the machine , and of course you can adjust the temperature to what ever suits youso far everything seems OK 

NB remember to set the washing machine on a cool wash (30/40) else the immersion in the machine will try and operate on the hot water you have fed in thro the mixer


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banjaxComment left on: 26 June 2012 at 3:51 pm

Cathy I have read the comments below and found this : However while the technology is interesting the price is sobering. Therefore I am wondering what else is out there.

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Cathy Debenham

Cathy DebenhamComment left on: 26 June 2012 at 2:59 pm

Banjax: the answer is very little. Hardly anyone makes hot feed any longer. I haven't done the research myself, but have had feed back from enough other people to think that it's not worth spending the time...

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Cathy Debenham

Cathy DebenhamComment left on: 26 June 2012 at 2:23 pm

Hi Banjax. Did you read the comments below? There are a few suggestions, and also a good argument as to why it's not necessarily a good idea (especially for the washing machine).

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banjaxComment left on: 26 June 2012 at 11:30 am

Can somebody please do an article on what is available in terms of hot fill dishwashers and washing machines ?

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Plumb Solar LTD

Plumb Solar LTDComment left on: 18 June 2012 at 1:26 pm

Just out of interest, we have installed a new Siemens dishwasher

(type- SN65M031GB)

And during installation were pleased to find it was able to accept pre-heated water from a renewable source - its just needed a simple programming change

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Cathy Debenham

Cathy DebenhamComment left on: 28 March 2012 at 7:59 am

Thank you for that really useful analysis Tony

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InglesideComment left on: 27 March 2012 at 8:54 pm

We went through all this last year, needing a new machine. Another reason for cold fill is that most washing is now done at 40, so if your hot water is 55 - 60, it's too hot. And mixing some cold in with the hot is way beyond the intelligence of the machines! Modern machines use less water, so less electricity to heat it up. Cycle times are longer, because a smaller quantity of water has to work harder, but the electricity consumed to 'wash' is much less than that to 'heat'. So there is a reduction in energy use, but it is very counter-intuitive! We did consider putting hot water into the cold feed, but then it will use hot water to rinse - not so smart. You could probably fit a clever valve, so that the first fill was hot water, and subsequent fills cold water, but you've still got the question of washing at a lower temperature than the hot water supply. We decided that it wasn't worth the hassle, but then, at 60+, we think that about a lot of things!


PS - we've got SHW and PV, so now tend to wash during the day to use the PV, rather than overnight to use the cheap rate.

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NorthGlosEPCComment left on: 22 March 2012 at 5:15 pm


Your comment about "payback" is interesting.

To a dergree I would agree with you. We don't seem to look at the payback in the same way when we buy say a car, a new kitchen or perhaps even a holiday. That is not in the same way we'll look at PV and solar hot water systems. Not sure I'd agree with you about the boiler though.

Thing is cars and kitchens are sort of status items whereas renewables are more practical. You are correct that renewables provide "esoteric benefits" and I'm certainly not opposed to the concept of renewable energy. We'll need a lot more installations in the future if we're to have any chance at all of correcting the problem.

But how are renewables marketed?

On the basis of the warm eco glow they'll give you or on the basis they are a sound financial investment?

As a DEA I'm often asked about renewables, mostly about solar PV but some about solar hot water. Not one person has asked about the environmental benefits such systems might afford. Every question is about the economics, the payback, how much FiT can I expect etc. etc. I always answer honestly and offered information based on that published by the energy saving trust and the like.

No one has said to me "regardless of investment potential I'll install a renewable simply to do my bit and cut Co2", not one.

Now although I'm all for renewables I find it amusing and mildly irritating that everyone who has a renewable can't stop telling you how wonderful an investment it is an how much money they are making and/or saving. Conveniently forgetting the several thousand they stumped up in the first place.

I'm more impressed that they did something to cut Co2, they did their bit. I applaud their action. So why must they often exaggerate the financial benefits and boast their investment prowess.

Don't know if you agree with my observations or not?

Never the less If it's given that investment potential and payback are the criteria for going forward with renewables how can it be overlooked?



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nnw49Comment left on: 22 March 2012 at 11:49 am

My washing machine is below the DHW cylinder, so there is about 2 litres of cold water before the hot water reaches it. I run this water off into a big jug and use it to water the house plants - that if the weather is sunny usually need some!

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SusieBooComment left on: 20 March 2012 at 2:12 pm



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Cathy Debenham

Cathy DebenhamComment left on: 19 March 2012 at 10:33 am

Thanks for your comments @NorthGlosEPC.

I'm interested in your comments about payback. I'm particularly interested in why it is that we only think about payback in relation to renewable energy and energy efficiency measures and not about other similar sized purchase we make. When we buy a boiler, a car, a new bathroom, an iPad, a designer handbag, or a family holiday, we know that it's never going to pay back. It's value is going to decrease and decrease, and then it's going to break and be worth nothing. Depending on how you use it, solar thermal can reduce your heating bills, and has other more esoteric benefits, such as the satisfaction of bathing in solar heated water, the knowledge that as gas prices continue to rise, you've got a built in buffer, and that you're emitting less carbon dioxide into the atmosphere.

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NorthGlosEPCComment left on: 18 March 2012 at 8:48 pm

Well solar hot water systems do work, they do provide some useful amounts of hot water for a good six months of the year even at our Northern latitudes. However if you look at the economics I'm afraid I'd agree with that professor of environmental policy. Most people (who would otherwise use mains gas water heating) installing such a system won't live long enough to see a payback even if energy costs double in coming years.

Now don't get me wrong this doesn't mean you should not install a solar hot water system, just be aware that it's an environmental or life style choice rather than a hard nosed economic choice. And from an environmental point of view I applaud anyone who does install such a system.

I certainly do agree about the hot fill washing machine. It makes sense to use solar hot water if you've got it available. It makes sense even if you have gas heated water so long as the supply is almost instantly available at the machine. But of course in most cases it's not, because usually there are a few metres of pipe work containing cold water going in first filling the machine before any hot water gets there.

Still even if this is the case it's no worse than only having only cold fill and using electricity to heat the water in the machine. So I say bring back hot and cold fill it cannot do any harm and I'm sure at least some systems will benefit from a point of view of energy efficiency.

Who knows there might be a bonus in that people with solar hot water who do lots of washing might even see an installation cost payback within their life time.

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Adam W

Adam WComment left on: 13 March 2012 at 12:25 am

Baumatic have a few models which are hot & cold fill e.g. BWR1206 and BWR1005

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HiltingburyComment left on: 9 March 2012 at 10:11 pm

The trouble is that modern machines are designed to use a lot less water (itself an important ecological step) so the hot fill never gets up to temperature before the machine closes the inlet off. All that succeeds in doing is filling the washing machine with cold water and putting more cold water into the thermal store. Not very efficient. Despite this logic we have restored our our old  Siemens washing machine to its hot fill since getting a solar thermal panel feeding our thermal store. To ensure we get hot water into the washing machine we run a local hot tap first and the washing machine uses a lot less electrical power to heat it up. Of course now we have solar pv as well  the electricity could be free (only use washing machine  at lunchtime on a sunny day). Confused? I certainly am!

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Kate_deComment left on: 9 March 2012 at 6:11 pm

Very interesting Linn! Why am I not surprised.....

I have also heard people say there are worries about excessively hot water potentially damaging some fabrics, so manufacturers pay it safe with cold fill, but no idea if that is really a factor.

As someone in the same situation as Alister I have fitted a hose to the hot water pipe, and I run in some hot water before I start the wash - through the soap tray. Yes, I do get wet feet occasionally and it is a bit approximate, but it feels better than nothing. 

Part of me rather hankers for my mother's old top-loading twin tub, then you could really be in control... maybe they'll come back eventually.

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nnw49Comment left on: 9 March 2012 at 1:07 pm

Feeling smug that my aged Bendix 1000 washing machine is hot/cold fill :)

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John Connett

John ConnettComment left on: 9 March 2012 at 11:39 am

I remember seeing a Beko washing machine (in one of the example houses at Ecobuild?) which was chosen because it had both hot and cold fill. Not easy to confirm from their web site ( but if you look at the manual for the WMB91442L Excellence it does appear to have two water connections (see page 9 of

Haven't checked the other models in their range.

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Linn Rafferty

Linn Rafferty from JTec Energy PerformanceComment left on: 9 March 2012 at 11:10 am

Oh yes, I recognise this - brought about by the need to comply with EU directives on energy performance of white goods, and methodologies for assessing energy performance that assumed water was heated by electricity (as is common in Europe). 

So now we can only buy 'efficient' washers, meaning they use electricity more efficiently by heating it from cold in the washer, compared to the (assumed) electrically heated domestic supply.

Maybe a black market in second hand washers will result!

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